Electrostatic discharge (ESD) is a known problem in the manufacturing and the using of integrated circuits (IC). Typically, transistors have thin oxides and insulating layers that can be damaged by the electrostatic discharge, and special care is required to protect the integrated circuits from the damage caused by the ESD. The corresponding circuits are known as ESD protection circuits.
ESD protection circuits, which form part of the IC, are normally connected to the input pads of the IC. ESD protection circuits may also be used at the outputs of the IC. The ESD protection circuits begin conducting or undergo breakdown to provide an electrical path to electrical ground (or to a power-supply rail) when ESD transient occurs and resulting in a very high ESD voltage.
Conventional ESD protection circuits usually have a large parasitic capacitance (CESD) that sometimes degrades the performance of the devices within the IC. For example, the ESD protection circuits typically use large MOS transistors, which have high capacitance values. An ESD protection transistor that is used in conventional ESD protection circuits has an enlarged drain area. Typically the drain extension is at least 2-3 times the minimum drain width that is permitted by the foundry process that is used. Drain extensions that are 10-15 times the minimum drain width have also been used. Typical values for CESD using this approach are 1.5 pF for a 3 kV rating. When the respective circuits are operated at high frequencies, the large parasitic capacitance of the ESD protection circuits significantly degrades the performance of the respective circuits, which may be for example, wireless transceivers operated at radio-frequencies.
The increased capacitance CESD also increases the noise that is contributed by the ESD protection circuits. As parasitic capacitance CESD increases, the noise coupling from the ESD protection circuit to the transceiver increases, which adversely impacts the operation of the transceiver. For example, the increased noise is amplified by the low noise amplifier in wireless transceivers.